Glazing panel carrying a coating stack

ABSTRACT

A glazing panel has a coating stack comprising in sequence at least a base antireflective layer, an infra-red reflecting layer, a top antireflective layer and a top coat layer comprising at least one material selected from the group consisting of nitrides, oxynitrides, carbides, oxycarbides and carbonitrides of the elements of groups lV b , V b  and VI b  of the periodic table.

GLAZING PANEL CARRYING A COATING STACK

This invention relates to glazing panels and particularly, but notexclusively, to solar control and/or low emissivity glazing panels whichare intended to undergo heat treatment following application to theglazing substrate of an optical filter in the form of a coating stack.

The invention relates more particularly to cases where a coating stackis applied to the glazing by a vacuum deposition technique, for exampleby sputtering or magnetron sputtering.

Multiple factors must be considered when designing coating stacks forglazing applications. These incdude not only the desired opto-energeticperformance of the coated glazing panel but also, for example, theabrasion resistance of the coating stack (to facilitate handling andprocessing), the stability and chemical durability of the coating stack(to facilitate storage under various conditions) and the tolerances ofthe control of the manufacturing process (to facilitate acceptablemanufacuring yields and consistency between product runs).

It is known to apply a top coat to a coating stack particularly in anattempt to increase the abrasion resistance and/or chemical durabilityof a coatings stack The use of metallic layers (for example of chromium,nickel chromium or zinc) or dielectric layers (for example titaniumoxide, silicon oxide, zinc oxide, silicon nitride, aluminium nitride)has been proposed in this context. However, many known non-metallic topcoats suffer from insufficient chemical durability, whilst knownmetallic top coats can have a number of disadvantages.

The present invention provides glazing panels, a method of manufacturingglazing panels and use of a top coat layer as defined in the independentclaims. Preferred embodiments are defined in the dependent claims.

The present invention may provide an advantageous combination of good:

chemical durability, especially where the top coat comprises a nitrideor an oxynitride

humidity resistance, particularly when the top coat comprises titaniumnitride

stability of manufacturing parameters

heat treatability

The top coat layer is preferably the outermost, exposed layer of thecoating stack.

The coating layers are preferably deposited by a vacuum depositiontechnique, particularly magnetron sputtering.

One advantage of the top coats of the present invention may be acombination of particularly good chemical durability during storage, forexample prior to heat treatment and/or assembly, with a facility tocontrol the manufacturing tolerances and production process. This may becombined with an ability to provide thermal protection to other parts ofthe coating stack during heat treatment With known metallic top coats:

Small variations in the thickness of a metallic top coat cansignificantly affect the properties of the heat treated coated glazingpanel and/or the heat treatment conditions that must be used, especiallyif the metal is relatively difficult to oxidise during heat treatment.

If a highly reactive metal is used then this will partially oxidise inair during storage prior to heat treatment of the glazing panel. Theextent of this oxidation may be difficult to control as it may dependupon the ambient temperature, the humidity and other storage conditionsand even the temperature of the glazing panel when it first enters theatmosphere at the exit of a vacuum coating line (the glazing paneltemperature will generally be lower for thicker substrates).

Consequently, It can be difficult to control the manufacturingtolerances and precise condition of an intermediate coated glazing panelthat arrives to be heat treated. The significant difference inrefractive index and/or extinction coefficient between a metal top coatbefore and after heat treatment may also renders the control of thethickness and heat treatment conditions critical to avoid unacceptablevariations in properties such as light transmittance, energytransmittance and colour in the heat treated glazing panel.

Fine adjustment and control of the manufacturing tolerance of thethickness of the top coats of the present invention may be less criticalto the variations of properties of the glazing panel; this mayfacilitate higher manufacturing yields and/or throughput. Furthermore,where the refractive indexes and/or extinction coefficients of the topcoats of the present invention are reasonably similar both before andafter heat treatment (for example with a variation in refractive indexat 550 nm of less than 1, 0.8, 0.6. 0.5, 0.4, 0,3 or 0.2 due to heattreatment and/or a variation in extinction coefficient at 550 nm of lessthan 1,5; 1,4, 1,3, 1,2, 1, 0.8, 0.6. 0.5, 0.4, 0,3 or 0.2 due to heattreatment), the tolerance of one or more properties, for example,luminous transmittance, energy transmittance, luminous reflection,colour in reflection, colour in transmittance, may be less prone tosignificant variation as a function of the manufacturing tolerances andstorage time and conditions of the intermediate product prior to heattreatment. The present invention may also facilitate the use of asubstantially identical coating stack on glazing substrates of differentthickness (for example, 2 mm, 4 mm, 6 mm, 8 mm thick glass sheets) whichrequire different conditions for correct heat treatment.

The use of a nitride or oxynitride top coat according to certainembodiments of the present invention may facilitate deposition control;this may especially be the case when a vacuum coater used to manufacturethe glazing panels has been exposed to the atmosphere for maintenanceand must be purged of air and/or water vapour contamination. Given thatair is about 80% nitrogen, air contamination may be less disruptive todeposition of these materials. The effect of air and/or water vapourcontamination on deposition in a reactive nitrogen and/or oxygencontaining atmosphere is less significant than equivalent contaminationin an inert (eg argon) sputtering atmosphere used for the deposition ofmetal layers as, in the latter case, the contaminants are the onlyreactive species present in the deposition atmosphere.

Where the glazing panel carries a coating stack having a single silveror other infra-red reflecting metal layer and having, for example, thestructure:

Glass

base antirefective dielectric layer

optional nucleation or barrier layer

infra red reflective metal layer

optional barrier layer

top antireflective dielectric layer

top coat layer

the base antireflective dielectric layer preferably has an opticalthickness in the range of 50 nm to 80 nm whait the combination of thetop antireflective dielectric layer and the top coat layer preferablyhas an optical thickness in the range 50 nm to 100 nm.

Where the glazing panel carries a coating stack having a double silveror other infra-red reflecting metal layer and having, for example, thestructure:

Glass

base antireflective dielectric layer

optional nucleation or barrier layer

infra red reflective metal layer

optional barrier layer

central antireflective dielectric layer

optional nucleation or barrier layer

infra red reflective metal layer

optional barrier layer

top antireflective dielectric layer

top coat layer

the base antireflective dielectric layer preferably has an opticalthickness In the range of 35 nm to 80 nm, the central antireflectivedielectric layer preferably has an optical thickness in the range 130 nmto 180 nm and the combination of the top antireflective dielectric layerand the top coat layer preferably has an optical thickness in the range40 nm to 80 nm.

The top coat layer may have a geometrical thickness of greater than orto equal to 10Å,15Å, 20Å or 25Å; it may have a geometrical thickness ofless than or equal to 100Å, 80Å, 70Å, 60Å or 50Å. The top coat layerpreferably has a geometrical thickness in the range 15 to 50Å, morepreferably 20 to 40Å particularly where it comprises a nitride or anoxynitride of titanium. Such thicknesses may provide an optimisation forproviding a desired corrosion resistance whilst simultaneously providinga top coating layer which will provide desired characteristics, forexample refractive index and/or extinction coefficient, after heattreatment.

The filter stack may comprise one or more barrier layers underlyingand/or overlying the infra red reflecting layer, as is known in the art.Barriers of, for example, one or more of the following material may beused. Ti, Zn, Cr, “stainless steel”, Zr, Nb, Ni, NiCr, NiTi, ZnTi andZnAl. Such barriers may be deposited, for example, as metallic layers oras sub-oxides (i.e. partially oxidised layers). Alternatively, nitridedbarrier layers may also be used. Each barrier layer may consist of asingle layer or may comprise two or more sub-layers which together formthe barrier layer. The barrier layer may comprise a first barrier layerin substantially metallic form, e.g. comprising nickel and chromium, andan overlying second barrier layer of a different composition from thefirst barrier layer (e.g. comprising titanium) which is in a formselected from the group consisting of oxides, sub-stoichiometric oxides,nitrides, sub-stoichiometric nitrides, oxynitrides andsub-stoichiometric oxynitrides.

Each antireflective dielectric layer may consist of a single layer ormay comprise two or more sub-layers which together form theantireflective dielectric layer. The top antireflective dielectriclayer, or at least portion of the top antireflective dielectric layerwhich contacts the top coat layer may be of a material other thansilicon nitride and/or other than aluminium nitride, it may comprise anoxide, for example an oxide comprising zinc and tin and/or zinc andaluminium.

The invention has particular utility in relation to glazing panelswhich,

when heat-treated will give a colour in reflection such that:

a* is between +2 and −10, preferably between 0 and −7; and

b* is between+2 and −15, preferably between 0 and −10;

or which

when heat-treated and assembled with a sheet of clear glass as doubleglazing units with the coating positioned inside the double glazing unitat position 2 (interior surface of exterior sheet of glass) or position3 (interior suface of interior sheet of glass) will give a colour inreflection seen from the outside such that:

a* is between 0 and −7, preferably between 0 and −4; and

b* is between +2 and −10, preferably between 0 and −7.

Preferably, the glazing panels, when heat treated and presented in theform of monolithic glazing and/or in the form of assembled doubleglazing units provide a substantially neutral colour in reflection.

The combination of properties that may be provided by the presentinvention have particular advantages in relation to heat treatable andheat treated glazing panels. Nevertheless, the invention may also beused in respect of glazings which are not heat treated. The term “heattreatable glazing panel” as used herein means that the glazing panelcarrying the coating stack is adapted to undergo a bending and/orthermal tempering and/or thermal hardening operation without the haze ofthe so treated glazing panel exceeding 0.5, and preferably without thehaze exceeding 0.3. The term “substantially haze free heat treatedglazing panel” as used herein means a glazing panel which has been bentand/or thermally tempered and/or thermally hardened and has a haze thatdoes not exceed 0.5 and which preferably does not exceed 0.3. Thethermal treatment may involve rising the temperature of the glazingpanel to a temperature exceeding 400° C., 450° C., 500° C., 550° C.,600° C., 650° C. or 700° C.

Heat treatment may provoke an increase in the luminous transmittance(TL) of the glazing panel. Such an increase in TL may be advantageous inensuring that TL is sufficiently high for the glazing panel to be usedin high light transmittance glazings, for example, in vehiclewindscreens or in architectural applications where the monolithic coatedglazing panel is desired to have a TL greater than about 55%, 60%, 65%,70%, 75%, 80% 85% or 90% or in double glazing units where the doubleglazing unit is desired to have a TL greater than about 55%, 60%, 65%,70%, 75%, 80% or 85%. TL may increase in absolute terms during heattreatment by, for example, greater than about 2.5%, greater than about3%, greater than about 4%, greater than about 5%, greater than about 8%or greater than about 10%.

The coating stack of the glazing panel of the present invention may besuch that if applied to a clear sheet of 4 mm glass it would give a TLmeasured with Illuminant C of greater than about 55%, 60%, 65%, 70%,75%, 80% 85% or 90% and/or an energetic transmittance (TE) (System Moon2) of greater than about 35%, 40%, 50%, 55% or 60%. The coating stackmay be responsible for a reduction of the TL of the glazing panel within the range 10 to 20%. The energetic transmittance (System Moon 2) ofthe glazing panel may be greater than 40%, 45%, 50%, 55%, 60% or 65%.Such properties or combinations of properties may be particularly usefulwhen the glazing panel is intended for use in low emissivityapplications.

The coating stack of the glazing panel of the present invention may besuch that if applied to a clear sheet of 4 mm glass it would give acombination of TL measured with Illuminant C and (TE) (System Moon 2)such that:

TL is greater than or equal to 70% and TE is less than or equal to 50%;or

TL is greater than or equal to 60% and TE is less than or equal to 42%;or

TL is greater than or equal to 50% and TE is less than or equal to 35%;or

TL is greater than or equal to 40% and TE is less than or equal to 30%.

Such a combination of properties may be useful where the glazing panelis intended for solar control applications.

The top coat layer of the present invention may undergo sometransformation or oxidation when stored in air, for example prior to anintended heat treatment operation. For example, where the top coat layeris initially deposited in the form of titanium nitride or titaniumoxynitride, at least the superficial portion of the top coat layer whichis exposed to air during storage may oxidise to titanium oxide. Asimilar effect may occur with other top coat layers of the invention.

Examples of the present invention will now be described with referenceto FIG. 1 and FIG. 2 which are cross-secions through glazing panelsprior to a bending and tempering operation (for ease of representation,the relative thicknesses of the glazing panel and coating layers are notshown to scale).

EXAMPLE 1

FIG. 1 shows a single Ag layer, heat treatable, coating layer depositedon a glass substrate by magnetron sputtering and having the followingsequential structure: Reference Geometrical Atomic number thicknessratios Glass substrate 10 4 mm Base antireflective layer 11 comprising:ZnSnOx 12 230 Å Zn/Sn ≈ 2 ZnSnOx 13 120 Å Zn/Sn ≈ 17 Ag (infra redreflective layer) 14 95 Å NiCr heat treatment barrier layer 15 10 Å Tideposition barrier layer 16 20 Å Top antireflective layer 17 comprising:ZnSnOx 18 130 Å Zn/Sn ≈ 17 ZnSnOx 19 210 Å Zn/Sn ≈ 2 Top coat layercomprising TiN 20 25 Å

In this type of structure, the Ag layer acts to reflect incident infared radiation and in order to fulfil this role must be maintained assilver metal rather than silver oxide and must not be contaminated byadjacent layers. The dielectric antireflective layers which sandwich theAg layer serve to reduce the reflection of the visible portion of thespectrum which the Ag layer would otherwise provoke. The heat treatmentbarrier serves to prevent degradation of the Ag layer during heattreatment of the glazing panel; it is usually at least partiallyoxidised in this process. The deposition barrier serves to preventoxidation of the heat treatment barrier during sputtering of theoverlying dielectric antireflective layer in an oxidising atmosphere;this barrier is at least partially oxidised during this process.

Properties of the glazing panel prior and subsequent to heat treatmentprocess are: Prior to heat Following heat Propertytreatment^(see Note 1 below) treatment^(see Note 2 below) TL (IlluminantC)   77% 87% TE (System Moon 2) 57.5% 67% haze 0.08 0.16 a* reflectance−4 −3 (coated side) (coated side) b* reflectance −17 −12 (coated side)(coated side) RE (System Moon 2)   20% 22% (coated side) (coated side)^(Note 1)Measured for monolithic glazing panel with coating prior toheat treatment^(Note 2)Measured following a tempering heat treatment process at 680°C. (furnace temperature) for 8 minutes Heat treatment preferably causessubstantially complete oxidationof the titanium nitride top coat layer.

The colour co-ordinates of the examples are particularly suited toarchitectural double glazing units as they give a neutral appearance inreflection.

Samples according to Example 1 were subjected prior to tempering to aCleveland Condensation resistance test and a Climatic Chamber test(Cycled condensation resistance test).

The Cleveland test consists of subjecting the coated glass to awater-saturated atmosphere at constant temperature. The samples havecondensation continually fomling on them and it is this condensationthat may cause surface degradation. A test cabinet (Cleveland) is placedin a room with an ambient temperature of 23° C. ±3. Care is taken toensure that draughts and solar irradiation do not interfere with thetest cabinet. The samples are mounted in a holder which forms the roofof the test cabinet. The floor of the test cabinet acts as thereceptacle for the quantity of water. The test cabinet is conditionedonly by heating the demineralised water on the floor with heatingresistances controlled by means of a thermocouple, keeping a temperatureof the water of 50°C. ±2. The samples are subjected to the test during24 hours.

The Climatic chamber test consists of subjecting the samples in anatmosphere maintained at 98% relative humidity to a continuous cycle ofa) increasing temperature from 45° C. to 55°C. over the space of onehour and b) subsequently decreasing the temperature from 55° C. to 45°C. over the space of one hour. This cycle is repeated for a period ofthree days. The test may be carried out in a 500 litre Weiss chamber.

Samples that have been subjected to each test are inspected for: a)punctual defects (diameter <0.5 mm) like needles, a limited density ofwhich may be acceptable; b) large defects such as spots of corrosion afew mm in diameter which are unacceptable; c) dissolution of the coatingwhich is unacceptable.

The following result were obtained: Comparative example without TestExample 1 top coat layer of Example 1 Cleveland No alteration More than20 spots per dm2 some of which of diameter greater than 1 mm Climaticchamber Less than 3 spots More than 20 spots per dm2 some per dm2 of aof which of diameter greater than diameter below 1 mm 0.5 mm Suitablefor long Yes Borderline duration storage

It is anticipated that variations to example 1 in which the material ofthe top coat layer Is selected from an alternative as defined in theclaims will have similar performances in the Cleveland and Climaticchamber tests.

The coating stack used in example 1 was also applied to other glasssheets having thicknesses of 4 mm, 6 mm and 8 mm. These sheets werestored in a variety of condition and for various durations (1 month forthe 6 mm, 3 months for the 4 mm, 5 months for the 8 mm samples) prior tobeing tempered and then assembled into double glazing units. Typicalproperties of these glazings were: Glass TL L R L Thickness (M) (M) a(M) b (M) (M) (DV) a (DV) b (DV) 4 mm 88.0 24.4 −1.6 −8.6 3.5 34.8 −1.4−4.0 6 mm 87.8 23.1 −1.3 −8.9 3.7 34.0 −1.2 −4.2 8 mm 86.4 23.3 −1.6−9.4 3.6 34.0 −1.2 −4.0

In which L, a and b are the colour coordinates on the Hunter scale, R isthe resistance per square, (M) indicates properties of the tempered,monolithic glazing measured from the coated side i.e. coating inposition 1 and (DV) indicates properties of a double glazing unitincorporating the tempered, coated glazing panel with a sheet of 4 mmclear glass, measured from the outside of the double glazing unit withthe coating in position 3

This demonstrates the stability of these properties with respect of theglass thickness and the storage conditions.

EXAMPLE 2

FIG. 2 shows a double Ag layer, heat treatable, coating layer depositedon a glass substrate by magnetron sputtering and having the followingsequential structure: Reference Geometrical Atomic number thicknessratios Glass substrate 10 2 mm Base dielectric 11 comprising: AIN 12 150Å ZnAlOx 13 160 Å Al/Zn ≈ 0.1 Ag 14 100 Å ZnAl overlying barrier 15 10 ÅAl/Zn ≈ 0.1 Central dielectric comprising ZnAlOx 16 790 Å Al/Zn ≈ 0.05Ag 17 110 Å ZnAl overlying barrier 18 14 Å Al/Zn ≈ 0.1 Top dielectriccomprising: 19 ZnAlOx 20 170 Å Al/Zn ≈ 0.05 AIN 21 85 Å Top coat layercomprising TiN 22 30 Å

in which ZnAlOx is a mnxed oxide containing Zn and Al deposited in thisexample by reactively sputtering a target which is an alloy or mixtureof Zn and Al in the presence of oxygen . The ZnAl barriers are similarlydeposited by sputtering a target which is an alloy or mixture of Zn andAl in a substantially inert, oxygen free atmosphere.

At least a portion of the overlying barriers 15, 18 is oxidised duringdeposition of their overlying oxide layers. Nevertheless, a portion ofthese barriers preferably remains in metallic form, or at least in theform of an oxide that is not fully oxidised to provide a barrier forsubsequent heat treatment of the glazing panel.

Properties of the glazing panel prior and subsequent to heat treatmentprocess are: Prior to heat Following heat Propertytreatment^(see Note 1 below) treatment^(see Note 2 below) TL (IlluminantA) 55% 76% TE (System Moon 2) 43% haze 0.07 0.35 (including pvb haze) a*−9 −7 (glass side) (glass side) b* +4 −6 (glass side) (glass side) RE(System Moon 2) 34% (glass side)^(Note 1)Measured for monolithic glazing panel with coating prior toheat treatment^(Note 2)Measured following a tempering heat treatment process at 650°C. (furnace temperature) for 10 minutes and lamination with a 0.76 mmlayer of pvb and a 2 mm sheet of clear glass

Heat treatment preferably causes substantially complete oxidation of thetitanium nitride top coat layer.

Prior to heat treatment, the coating stack of Example 2 also performswell in the Cleveland and Climatc chamber tests.

Additional layers may be introduced above, below or between the filmstacking arrangement if desired without departing from the invention.

GLOSSARY

Unless otherwise indicated by the context, the terms listed below havethe following meanings in this specification: a* colour co-ordinatemeasured on the CIELab scale at normal incidence Ag silver Al aluminiumAl2O3 aluminium oxide AlN aluminium nitride b* colour co-ordinatemeasured on the CIELab scale at normal incidence Cr chromium haze thepercentage of transmitted light which in passing through the specimendeviates from the incident beam by forward scattering, as measured inaccordance with the ASTM Designation D 1003-61 (Reapproved 1988). infrared a material that has a reflectance higher than the reflectance ofsodalime glass in reflecting the band of wavelenghts between 780 nm and50 microns material Na sodium Nb niobium NiCr an alloy or mixturecomprising nickel and chromium NiTi an alloy or mixture comprisingnickel and titanium RE energetic the solar flux (luminous andnon-luminous) reflected from a substrate as a reflection percentage ofthe incident solar flux selectivity the ratio of the luminoustransmittance to the solar factor i.e. TL/TE Si02 silicon oxide Si3N4silicon nitride SnO2 tin oxide Ta tantalum TE energetic the solar flux(luminous and non-luminous) transmitted through a substrate as atransmittance percentage of the incident solar flux Ti titanium TLluminous the luminous flux transmitted through a substrate as apercentage of the incident transmittance luminous flux Zn zinc ZnAl analloy or mixture comprising zinc and aluminium ZnAlOx a mixed oxidecontaining zinc and aluminium ZnAlOy a partially oxidised mixturecomprising zinc and aluminium ZnO zinc oxide ZnTi an alloy or mixturecomprising zinc and titanium ZnTiOx a mixed oxide containing zinc andtitanium ZnTiOy a partially oxidised mixture comprising zinc andtitanium Zr zirconium

1. A glazing panel carrying a coating stack comprising in sequence atleast: a glass substrate a base antireflective layer an infra-redreflecting layer, a top antireflective layer a top coat layer in whichthe glazing panel is adapted to be heat treated and in which the topcoat layer comprises at least one material selected from the groupconsisting of nitrides, oxynitrides, carbides, oxycarbides andcarbonitrides of the elements of groups IVb, Vb and VIb of the periodictable. 2-14. (canceled)
 15. A glazing panel in accordance with claim 1which is adapted for assembly in a double glazing unit.
 16. A glazingpanel in accordance with claim 15, in which the glazing panel is adaptedfor assembly in a double glazing unit with the coating stack in position3.
 17. A glazing panel in accordance with claim 15, in which the glazingpanel is adapted to be heat treated prior to assembly in a doubleglazing unit.
 18. A double glazing unit comprising at least oneheat-treated glazing panel in accordance with claim
 1. 19. A doubleglazing unit in accordance with claim 18, in which the double glazingunit gives a colour in reflection seen from the outside such that a* isbetween 0 and −4 and b* is between 0 and −7.
 20. A double glazing unitin accordance with claim 18, in which the double glazing unit has aluminous transmittance of greater than 70%.
 21. A method ofmanufacturing a heat treated glazing panel comprising the steps of, inorder: a) depositing a coating stack on a glass substrate to provide anintermediate glazing panel comprising, in sequence, at least: a glasssubstrate a base antireflective layer an infra-red reflecting layer,[[and]] a top antireflective layer, and a top coat layer which comprisesat least one material selected from the group consisting of nitrides,oxynitrides, carbides, oxycarbides and carbonitrides of the elements ofgroups IVb, Vb and VIb of the periodic table. b) subjecting the coated,intermediate glazing panel to a heat treatment process in air at atemperature of greater than 550° C.
 22. A method in accordance withclaim 21 comprising the steps of: a) depositing a coating stack on aglass substrate to provide an intermediate glazing panel with a luminoustransmittance of greater than 75%; b) subjecting the coated,intermediate glazing panel to a heat treatment process in air at atemperature of greater than 550° C.; c) providing a heat treated glazingpanel with a luminous transmittance of greater than 85%.
 23. A method inaccordance with claim 21, in which heat treatment of the intermediateglazing panel causes substantial oxidation of the top coat layer.
 24. Amethod in accordance with claim 21, in which the luminous transmittanceof the heat treated glazing panel following the step of heat treatmentis greater than the luminous transmittance of intermediate glazing panelby at least 8%.
 25. A method in accordance with claim 21, in which theintermediate heat treated glazing panel comprises a glazing panel inaccordance with claim
 1. 26. Use of a top coat layer which comprises atleast one material selected from the group consisting of nitrides,oxynitrides, carbides, oxycarbides and carbonitrides of the elements ofgroups IVb, Vb and VIb of the periodic table to enhance chemicaldurability before heat treatment of a heat treatable coated glazingpanel having at least one metallic infra red reflecting coating layersandwiched between dielectric layers.
 27. A method of manufacturing aglazing panel having a haze of less than about 0.5 comprising the stepof subjecting a glazing panel in accordance with claim 1 to a temperingand/or bending operation at [[at]] least 570° C.
 28. A glazing panel inaccordance with claim 1 , including at least one of the followingcharacteristics (a) through (c): (a) the coated glazing panel has aluminous transmittance of greater than 70%; (b) the coated glazing panelprovides a substantially neutral colour in reflection; (c) a heattreatment provokes an increase in the luminous transmittance of theglazing panel.
 29. A glazing panel in accordance with claim 1, includesat least one of the following (a) and (b): (a) at least one of theantireflective layers comprises an oxide; and (b) at least one of theantireflective layers comprises a mixed oxide of zinc and one or more oftin, aluminium and titanium.
 30. A glazing panel in accordance withclaim 1, the base antireflective layer comprising at least one layercomprising a mixed oxide of zinc and tin.
 31. A glazing panel inaccordance with claim 1, the base antireflective layer consistingessentially of mixed oxides of zinc and tin.
 32. A glazing panel inaccordance with claim 1, wherein the top antireflective layer comprisesat least one layer comprising a mixed oxide of zinc and tin.
 33. Aglazing panel in accordance with claim 1, wherein the top coat includesat least one of the following (a) through (d): (a) the top coat layerconsists essentially of a material selected from the group consisting ofnitrides and oxynitrides of the elements of groups IVb , Vb and VIb ofthe periodic table; (b) the top coat layer consists essentially of amaterial selected from the group consisting of titanium nitride,chromium nitride, zirconium nitride, titanium oxynitride, chromiumoxynitride, zirconium oxynitride and mixtures thereof; (c) the top coatlayer comprises titanium nitride; (d) the top coat layer has ageometrical thickness in the range 15 to 50Å.
 34. A glazing panel inaccordance with claim 1, further including a barrier layer between theinfra-red reflecting layer and the top antireflective layer.
 35. Aglazing panel in accordance with claim 34, in which the barrier layerincludes at least one of the following (a) through (c): (a) the barrierlayer comprises a first barrier layer in substantially metallic form andan overlying second barrier layer of a different composition from thefirst barrier layer which is in a form selected from the groupconsisting of oxides, sub-stoichiometric oxides, nitrides,sub-stoichiometric nitrides, oxynitrides and sub-stoichiometricoxynitrides; (b) the barrier layer comprises a first barrier layercomprising nickel and chromium and an overlying second barrier layercomprising titanium; (c) a barrier layer selected from the groupconsisting of a barrier layer comprising nickel and chromium, a barrierlayer comprising titanium, and a barrier layer comprising a firstbarrier layer comprising nickel and chromium and an overlying secondbarrier layer comprising titanium.
 36. A glazing panel in accordancewith claim 1, including: the base antireflective layer comprising atleast one layer comprising a mixed oxide of zinc and tin; a barrierlayer between the infra-red reflecting layer and the top antireflectivelayer; the top antireflective layer consisting essentially of mixedoxides of zinc and tin; and the top coat layer comprises at least onematerial selected from the group consisting of nitrides, oxynitrides,carbides, oxycarbides and carbonitrides of the elements of groups IVb ,Vb and VIb of the periodic table.
 37. A glazing panel in accordance withclaim 1, in which the glazing panel consists essentially of, insequence, a glass substrate a base antireflective layer consistingessentially of mixed oxides of zinc and tin; an infra-red reflectinglayer, a barrier layer selected from the group consisting of a barrierlayer comprising nickel and chromium, a barrier layer comprisingtitanium, and a barrier layer comprising a first barrier layercomprising nickel and chromium and an overlying second barrier layercomprising titanium; a top antireflective layer consisting essentiallyof mixed oxides of zinc and tin; and a top coat layer consistingessentially of titanium nitride.